A tooth is comprised of an inner dentin layer and an outer hard enamel layer that protects the dentin layer. The enamel layer of a tooth is naturally an opaque white or slightly off-white color. The enamel layer can become stained or discolored. The enamel layer of a tooth is composed of hydroxyapatite mineral crystals that create a somewhat porous surface. It is believed that the pores of the enamel layer allow staining agents and discoloring substances to permeate the enamel and discolor the tooth.
Many substances that a person confronts or comes into contact with on a daily basis can “stain” teeth. In particular, foods and fluids such as tea and coffee that one consumes tend to stain one's teeth. These products or substances tend to accumulate on the enamel layer of the tooth and form a pellicle film over the teeth. These staining substances can then permeate the enamel layer. This problem occurs gradually over many years, but imparts a noticeable discoloration of the enamel of one's teeth.
Abrasive agents (for example, silica-based agents) are often used in oral care compositions for stain removal. However, brushing with compositions comprising such agents often leads to enamel damage. This can cause problems such as dentinal hypersensitivity. Peroxide-based agents are also known to have teeth whitening effects. However, peroxide-containing compositions are often unstable and lose whitening efficacy during storage. It is also known to use polyphosphate compounds (for example, pyrophosphates, tripolyphosphates and hexametaphosphates) for stain removal. However, such polyphosphate compounds may interfere with enamel remineralization (i.e. the reformation of crystalline hydroxyapatite—the main constituent of enamel) due to their crystal growth inhibiting properties.
Therefore, it would be desirable to provide further methods of stain removal and prevention which overcome these disadvantages.